Space discharge system



June 24,1930; A,A,OSV'VALDE AL 7 1,768,418

SPACE DISCHARGE SYSTEM g /2h 20 if LEE Filed Dec. 1924 INPUT II; 4OUTPUT //7ve/2f0r s--1 fifty/A flan Mi CST Patented June 24,

"STATES Nil" ARTHUR A. osWALD, or EAsT ORANGE, Ann mm: c.- soHELLENG,onMILLBUnn, New

JERSEY,

nssrenons To 'WES'IERN nLncTn-rc coiarANY, .moonrona'rnn, or new YORK,N. Y., A. CORPGBATION OF NEW YORK SPACE ms'cnanen sYsTEM Applicationfiled December 4, 1924. Serial No. 758,805.

This invention relates to prevention of undesired oscillations in anelectric system includmg parallel connected electrlc discharge devices.It is particularly applicable to carrier wave signaling systems in whichthree electrode discharge devices are used to supply carrier waves orimpulses of high power and high voltage to a transmitting circuit.

As is well known, when electric discharge devices each comprising aclosed vessel having an electronic cathode, an anode and controlelectrode 01' grid, are connected in parallel to supply energy to a loadcircuit, there is a tendency toward the production of tree oscillationsor singing in the system com prising the devices and their associatedcircuits. These oscillations are especially undesirable in cases wherethe system is to be used faithfully to reproduce high frequency wavesimpressed on the input circuit of the devices, as in carrier si nalingsystems; since, among other disadvantages their production oftenprevents the system from operating at the desired frequency, causesdistortion oi the form of the wave to be repeated, wastes energy bydiverting it from a useful purpose thereby reducing the efficiency ofthe system and causes serious overheating of the circuit conductors andlead-in wires for the electrodes of the discharge devices, whereby thedevices are liable to be destroyed. I a I 7 It is generally acceptedthat the production of undesired or spurious oscillations is due to thecyclic transfer of energy from the output circuits of the devices totheir input circuit, the amplitude and phase of this energy relative tothat traversing the output circuits being such as to set up and maintaina current flowingin the system, the frequency of which is determined bysome or all of the inherent reactances of the system. The inherentr'eactances of a system of this kind may be defined as consisting of thesmall inductances of the leads connecting their grids, thesmallinductances of the leads connecting their plates, and the internalgrid-filament, grid-plate and filamentplate capacities of the parallelconnected devices, as well as the difl'ere'nt inductances small powerlow voltage simple installations.

Owing to the complexities involved in placing a large number of tubes insimple parallel relation it has been found advisable to group the tubesinto separate banks and then to connect the banks in parallel relation.

When this is done it has been found that there are several'possiblemodes of singing which become effective as the power is in creased. I 7

One mode of singing which may be styled intra-tube singing has beenreadily eliminated by the proper geometrical positioning of the tubesand their associated circuits.

Inter-tube singing, that is singing vresulting from the cooperation of apair, or groups of tubes in a bank has been substantially eliminated bythe arrangements shown and described in the application of Oswald andSchelleng, Serial No. 645,027 filed June 13,

1923. Forthat purpose the system there disclosed includes a network ofinductances and resistances (fragmentarily shown in the bank 9)interconnecting the plates or the grids or both the plates and the gridsof the tubes comprising the bank. When this was done, however, it wasfound that the tubes in the two banks still coacted to produce interbanksinging. a

Interbank singing may be defined as singingresulting from thecooperation of r a plurality of banks oftubes and has been eliminated inpractice. bya system shown and described in an application of J. G.

Sche'lleng, Serial No. 700,554, iiled March] 20, 11924, in whichaninterbank reactor is used in the common grid or the common plateconnections of the two banks of tubes. The interbank'reactor comprises,an inductance having a resistance connected in parallel thereto and hasits terminals connected to the common conductors or bus bar's c0nnectingthe corresponding electrodes of the discharge devices of the differentunits. Intermediate points of the elements of the re actor device areconnected together and to the common circuit connecting the input oroutput apparatus to the space discharge systerm.

This arrangement was found to eliminate the interbank singing but whenhigh power is used, such as 200 k. W. in the output circuit in anamplifier consisting of two blanks of ten tubes each, very troublesomesinging was still noted.

In a'particular installation such as noted above which was operated toamplify a speech band in the general-region of 57,000 cycles, it wasfound that spurious oscillations were being set up at a frequency ofabout 1,100,000 cycles greatly interfering with the operation of thesystems. After investigation it was concluded that these oscillationsresulted from the coaction of inductances and capacity to ground ofcertain elements and leads in the input and output circuits.

Whatever the nature or cause of these undesired oscillations, theirpresence, for the reasons given above is detrimental to the properoperation of the system.

Consequently, a general object of this invention vis to eliminateundesired high frequency oscillations in a high power carrier wavetransmission system. A further ob ject is to improve the quality of thetransmitted signal. A still further object is to reduce the losses,increase the overall efficiency and reduce interruptions to service in aradio transmission system employing high power vacuum tube arrangements.

A particular object is the prevention of singing in a high power vacuumtube installation consisting of a bank of tubes or a plurality of banksof tubes to which previous methods of preventing intra-tube, intertube,and interbank singing have been applied.

A special object of the invention is the accomplishment of the abovenamed objects in a push-pull amplifier system.

The circuit arrangement so far found most useful in accomplishing theobjects of the invention consists of a resistance and a capacityconnected between the common grid connections of the high poweramplifier banks and ground. This path is of high impedance for signaland carrier frequencies but is of low impedance for the undesiredoscillations. This path may be regarded as shunting to ground anddissipating the undesired oscillations or alternatively as altering theconstants of the oscillation circuit in which the spurious oscillationstend to occur so that it is incapable of producing free oscillations.

The novel features which are believed to be characteristic of thisinvention will be pointed out with particularity in the claims appendedhereto. The invention itself, however, as to its objects and advantages,the details of its organization and the mode of its operation will bebetter understood by referring to the following description taken inconnection with the accompanying drawing in which Fig. l is adiagrammatic rep resentation of a radio signaling system embodying oneform of this invention and Fig. 2 shows this invention applied to apushpull amplifier.

In the system shown in Fig. 1, a modulator M is supplied by current ofsignal frequency from source S and by a current of carrier frequencyfrom the source 0, which currents are combined to form a modulatedcarrier current. This modulated current is then impressed upon filter Fwhich may be designed to pass the side bands and carrier frequencycomponent and suppress the components of signal frequency. Filter F,however, is preferably designed to pass only one side band. Thecomponents passed by this filter are impressed upon amplifier A whichmay consist of any number of stages but in this particular systemconsists of three stages of amplification. The output energy from thisamplifier is impressed. by means of transformer 1 upon an amplifyingdevice 2 comprising a fourth stage of amplification. The output energyfrom the device 2 is impressed upon the fifth stage of amplificationconsisting of banks 9 and 10 through conductors 3 and 5 and tunedcoupling circuit 4, in which R, is an inductive resistance of 100 ohms;L is an inductance of such value that its impedance at 57,000 cyclesequals 100 ohms; C and L in connection with R and L are of such valuethat the circuit is resonant at 57,000 cycles.

Resistance R across the secondary of transformer 1, equal to one halfthe minimum input impedance of tube 2 serves to stabilize the outputimpedance of amplifier A when tube 2 is operating at substantiallymaximum output.

The details of the apparatus and manner of connection of the fifth stageof amplification are described in the application of Oswald andSchclleng referred to above. Space current is supplied to the anodes ofthe fourth and fifth stages from source 21 through inductances 17 and 18which offer a high impedance to high frequency currents. Condenser 25serves as a by-pass around source 21 for high frequency currents. Gridpotential is applied to amplifiers 2 and 9 by source 24 and filters Fand F respectively. Potentiometers 22 and 23 of 2,000 ohms and 34; ohmsresistances respectively, provide means for adjusting the grid potentialapplied from source 24. The grid polarizing potential is suppliedthrough filters F and lli) 'F which are so designed that the impedancebetween the grid connection and the ground terminal is low for allfrequencies except zero (D. C.) to prevent a blocking action vhich mightotherwise occur under certain conditions. Although the values of theelements of these filters may be varied over wide limits the followingvalues have been found useful. C and C 2 mf.; C i not; C and C mi; L andL 1 to 5 henries; L 1 to 5 milhenries. The direct cur- I rent to thegrid in the fifth stage is from .5 to 2 amperes, and in order to preventdistortion caused by changes in the grid polarizing potential whichresult from variations inthis current, the impedance of thepotentiometer 28 is made relatively low. About 2.5 k. w. is expended inthe potentiometer, the grid polarizing potential being of the order of290 volts. The current flowing through the potentiometer is five timesthe grid current.

An interbank reactor 6 is shown in the grid leads of banks 9 and 10. Itmay, however, be inserted in the plate lead of the banks or omitted ifnot needed in the particular apparatus to prevent interbank singing.Switches 7 and 8 are shown for cutting this reactorout of circuit. Thedetails of the reactor 6 and its manner of connection are fully setforth in the applicationof Schelleng above referred to.

The output energy from banks 9 and 10 is' impressed upon the antennacircuit 13 by means of tuned coupling circuit 19 and radiated therefrom.Condenser 12 serves as a blocking condenser to prevent short circuitingthe source 21 to ground. Capacity 14 in connection with inductance 20will operate as a tuned circuit to increase the efficiency of thesystem.

An impedance path comprising resistance 15 of 100 ohms and condenser 16of 2,000 mmf. capacity is connected between the common grid. lead 5 andground. Condenser 16 presents high impedance to currents of signal andcarrier frequencies but will be or low impedance to high frequencycurrents such as are present as undesired oscillations which will beconducted to ground through resistance 15. In other words the constantsof the oscillation cricuit which result in.

Reactance coil 28, connected across the ing the parallel opposingreactance of the two halves of coil 28, forming a shunt tothe gridfilament circuit at thetuhes, is tuned to the frequency at which singingoccurs. In a particular installation this frequency was estimated tobe11,000 kilocycles. Re sistance introduces a damping inpedence to theseoscillations which prevents them building up.

Although the 7 effect of different elements in a circuit cannot beaccurately discussed without a consideration of the other ele ments, thefunction ofthe condenser and resistance can be qualitatively indicatedas follows: In order to have sustained oscillations in any closed path,it is necessary that the sum of the impedances around that path be zero,i. e., the reacta'nces must be zero and the resistances must be zero. Atfrequencies for which there 1s a tendency for spurious oscillations theinput impedance of the power bank has a negative resistance component.To prevent this oscillation from occurring by means of a modification inthe grid circuit it is necessary to design the latter such that itsimpedance looking back from the tube has such values throughout thenegative resistance frequency band that the above conditions are notmet. That is, either (1), it must have a positive resistance greaterthan thenegative component of the input impedance or (2), the reactancemust not balance out that of the input impedance. The function of theresistance is to meet condition (1). In case the resist an'ce is notused, the condenser maybe large enough to prevent oscillations bymeeting condition (2) by effectually short circuiting the input circuit.Another function of the condenser is to avoid short circuiting the inputcircuit at the frequency of opera tion. It has been found advisable touse the condenser and resistance in combination for this reason.

It is presumed that capacity 14 at the high frequency of the spuriousoscillations has an inductive reactance which coacts with the inductivereactance of tuned circuit 4 of possibly with other elements con nectedto the grid circuit of amplifier 9, 10 and in connection therewithcauses oscillations. The capacity to ground of condenser 12 becomesnoticeable at high frequencies and may coact with inductance of capacity14 to form a tuned circuit in'its plate lead. In a particular case ithas been found advisable to construct, capacity lt of a large number ofsmall units. The leads connecting these units with each other and lUl)with adjacent apparatus have an appreciable inductance which becomeseffective at high frequencies to cause oscillations. Although all leadsare kept as short as possible, they necessarily have some inductance athigh frequency and it is these inductances which are believed to causethe oscillations above referred to. Whatever may be the cause of theseoscillations, however, impedance devices 15 and 16 eliminate them.

It has been found advisable to employ the resistance 15 and condenser 16in addition to the means for preventing intra-tube, intertube andinterbank singing, it having been found that, although applying meanssuch as the resistance-inductance network illustrated in part in thebank 9 and the interbank reactor stopped certain types of spuriousoscillations, a new oscillating condition persisted. This conditioncontinued troublesome until eliminated by an impedance path comprisingelements 15 and 16.

Although this invention has been shown and described as applied toparticular systems, it should be understood that it is not limited tothis system but only in accordance with the spirit of the invention asdefined in the following claims.

What is claimed is:

1. In a space discharge system, including a plurality of unitscomprising one or more tubes, the method of preventing the production ofundesired oscillations of a frequency higher than that of the desiredwaves in the system which comprises introducing a path to groundconsisting of high impedance for waves of desired frequency and lowimpedance for said undesired oscillations.

2. A space discharge system comprising a plurality of space dischargeunits, means comprising a high impedance path for desired oscillationsand a low impedance path extending between certain elements of saidunits and ground for undesired oscillations of a frequency higher thanthat of the desired waves.

3. In a space discharge system comprising a plurality of space dischargeunits having electrodes, means comprising a high impedance path fordesired oscillations and a low impedance path for undesired oscillationsof a frequency higher than that of the desired waves connecting theelectrodes of said units to ground.

4. In a space discharge system comprising a plurality of space dischargeunits, means comprising a resistance and a capacity in series havinghigh impedance for desired oscillations and low impedance for undesiredoscillations of a higher frequency than that of the desired oscillationsadapted to form a shunt path for said undesired oscillations.

5. In a space discharge system comprising a plurality of space dischargedevices having electrodes, means comprising a resistance and a capacityin series in the alternating current portion of the system adapted toconnect said electrodes to ground whereby a positive decrement ismaintained for undesired oscillations.

6. In a space discharge system comprising a plurality of space dischargedevices having electrodes, means connecting some of said electrodes toground comprising a capacity and a resistance in series in thealternating current portion of the system, said capacity adapted tooffer high impedance to desired oscillations and low impedance toundesired oscillations, and said resistance adapted to dissipate saidundesired oscillations.

7. In a space discharge system, a plurality of space discharge deviceshaving electrodes,

means connecting some of said electrodes to ground, comprising acapacity and a resistance in series adapted to offer high impedance todesired oscillations whereby they are caused to traverse the spacedischarge devices and low impedance for undesired oscillations of ahigher frequency than that of the desired oscillations whereby they arepassed through said resistance and dissipated.

8. A system comprising a plurality of space discharge devices connectedin parallel, a system of impedance elements connecting certainelectrodes of said devices including at least one grid electrode withcertain electrodes of other devices to prevent oscillations, and acapacity in series with a resistance connected between the grids of saidelements and ground.

9. A system of space discharge devices comprising a plurality of tubes,a source for supplying signal waves to said tubes, an inductance and aresistance connected in parallel between at least two of said tubes andwith respect to said source, and a path includin a resistance extendingfrom an intermediate point of said inductance to ground.

10. A combination in accordance with claim 9 in which said path includesa condenser.

11. A combination in accordance with claim 9 in which said path includesa condenser and a resistance in series.-

12. A system of space discharge devices comprising a plurality of tubes,a circuit coupling certain of said tubes including inductance andcapacity, and means to prevent the production of undesired oscillationsincluding a path to ground from an intermediate point in saidinductance, said path containing a resistance element.

13. A system of space discharge devices comprising a plurality of tubes,a circuit coupling certain of said tubes including inductance andcapacity, and means to prevent the production of undesired oscillationsincluding a path to ground from an intermediate point in saidinductance, said path containing a condenser.

14. A system of space discharge devices comprising a plurality oftubes,-a circuit coupling certain of said tubes including inductance andcapacity, and means to prevent the production of undesired oscillationsincluding a path to ground from an intermediate point in saidinductance, said path containing a condenser and a resistance in series.

In Witness whereof, We hereunto subscribe our names this lst'jflay ofDecember, A. D.,

ARTHUR A. OSWALD, JOHN C. SCI-IELLENG.

